1. Field of the Invention
The present invention relates to a slip ring device and more specifically to a slip ring device preferably for use in transmitting signals in a mechanism including a swing unit, such as, for example, a monitoring camera or a robot mechanism.
2. Description of the Related Art
A conventional slip ring device extensively used in flexing portions or rotating portions such as joint portions of an industrial robot can maintain connection and electric conduction between a fixed-side wiring line and a rotating-side wiring line at all times regardless of continuous rotation or reverse rotation. The slip ring device is designed to avoid disconnection of a wiring line otherwise caused by complex layout or bending fatigue. More specifically, as shown in FIGS. 11 and 12 of Japanese Patent Application Publication No. 2003-116249, a known slip ring device includes a rotating shaft unit having a rotating shaft and a plurality of electricity-collecting rings fixed to the rotating shaft and a fixed unit having a case and electrically conductive brushes and terminals, both of which are connected to the case. Lead lines connected to the electricity-collecting rings are led out to the outside through an insertion bore of the rotating shaft. The electrically conductive brushes connected to the terminals of the fixed unit are kept in sliding contact with the electricity-collecting rings at all times, thereby electrically interconnecting the shaft-side lead lines and the case-side terminals.
In the meantime, a monitoring camera is used as an image signal input unit in a warning system for crime and disaster prevention. A slip ring is arranged on a support base for rotatably supporting the monitoring camera, so that signals can be transmitted between the monitoring camera and the support base through the slip ring. For instance, Japanese Patent Application Publication No. 2005-278071 discloses a known slip ring coupling structure for a monitoring camera and a structure for rotatably and concentrically coupling a first rotating shaft within a slip ring attached to a base plate with a second rotating shaft fixed to a camera support base.
In recent years, due to the demand for an increased image quality, a high-definition monitoring camera is available in a monitoring camera market. In the state-of-the-art monitoring cameras, image information of 200,000 to 400,000 pixels is transmitted at a transmitting speed of about 100 Mbps. In the high-definition monitoring camera of the kind stated above, there is a need to rapidly transmit high-definition image data of 1,000,000 pixels or more, or full-high-definition image data of 2,000,000 pixels or more, at a transmitting speed of about 1 Gbps or more. The conventional slip ring device mentioned above has a structure in which the lead lines are just electrically connected to the brushes and the electricity-collecting rings making sliding contact with each other at all times. Three signal transmission routes, i.e., a lead line route, a slip ring route and a lead line route, are just serially connected to one another with no consideration given to impedance consistency. Therefore, high-speed high-frequency signals such as image signals of a high-definition camera are reflected in the joints of the signal transmission routes and thus are not smoothly transmitted through the signal transmission routes. This leads to increased signal attenuation and reduced reliability.